For a great number of heat exchanging tubes (heat transfer tubes) provided in a shell (body) of a heat exchanger, carbon steel is mainly used in view of heat transfer efficiency and material cost. There are a bare-type and a fin-type for heat transfer tubes. The fin-type is used for a heat transfer tube since the fin-type has higher heat transfer efficiency.
The heat exchanging performance of the heat exchanger is deteriorated by ash and soot adhering to and depositing on the heat transfer surface of the heat transfer tube during continuous operation. When ash and soot included in flue gas adhere to and deposit on the surface of the heat transfer tube, the ash and soot form a bridge in a gap between heat transfer tubes. The bridge narrows the flue gas passage between the heat transfer tubes, thereby obstructing the flow of the flue gas flowing through the group of heat transfer tubes, resulting in the rise of pressure loss of the flue gas. Further, moisture (mist) in the flue gas adheres to the beat transfer tube, wetting the heat transfer tube, which is one of causes of corrosion.
There are methods for removing the ash and soot adhering to the heat transfer tube such as a method of shaking off the ash and soot adhering to the heat transfer tube by the impact of a fallen steel ball hitting the heat transfer tube, a method of forcibly burning the soot adhering to and depositing on the outer circumferential surface of the heat transfer tube using a heating wire attached to the outer circumferential surface of the heat transfer tube, and a method of removing the ash and soot adhering to the surface of the heat transfer tube by blowing steam or air by a soot blower (e.g., see Patent Literatures 1 to 3).
There are methods of preventing corrosion of a heat transfer tube by covering the heat transfer tube using a resin tube or a method of applying a coating on the heat transfer surface of the heat transfer tube (e.g., see Patent Literature 4).